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Kirt Blattenberger - RF Cafe Webmaster

Copyright: 1996 - 2024

Webmaster:

    Kirt Blattenberger,

    BSEE - KB3UON

RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while typing up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived...

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Capacitor Dielectric Properties

The question arises all the time concerning which capacitor type to use for a particular application. This table provides a guideline for starters, but is in no way exhaustive. (DA = dielectric absorption)

The unofficial temperature coefficient designations for the capacitors are as follows: The temperature coefficient is given as "P" for positive, "N" for negative, followed by a 3-digit value of the temperature coefficient in ppm/°C. For example "N220", is -200 ppm/°C, and "P100" is +100 ppm/°C. The one exception in this system is "NPO" where an "O" instead of "0" is used, but quite a number of people use "NP0." In any event "NPO" means stable with temperature.

Dielectric Type DA Advantages Disadvantages Uses
NPO Ceramic

(COG)

<0.1% Tight tolerance

High Q factor, low K

Small case size

Inexpensive

Good stability

Wide range of values

Low inductance

DA generally low, but may not be specified

Limited to small values (10 nF)

Low loss, timing and tuning applications
Monolithic

Ceramic

(High K)

>0.2% Low inductance

Wide range of values

Poor stability

Poor DA

High voltage coefficient

 
X7R  (BX)

(Barium Titanate)

  Inexpensive

Low DA available

Wide range of values

Smaller case size

Damaged by temperature

    >+85° C

Loose tolerances

High inductance

Bypassing, coupling, and frequency discrimination circuits
Z5U & Y5V   Smallest case size

Very large values

Damaged by voltages

    >25 WVDC

Very loose tolerances

Bypassing and coupling
Polystyrene 0.001%

to 0.02%

Inexpensive

Low DA available

Wide range of values

Good stability

Damaged by temperature

    >+85° C

Large case size

High inductance

Timers and filters
Polypropylene 0.001%

to 0.02%

Inexpensive

Low DA available

High dielectric strength

Wide range of values

Negative TC

Damaged by temperature

    >+105° C

Large case size

High inductance

Stable oscillators and filters, sample and hold circuits and pulse handling circuits
Teflon 0.003%

to 0.02%

Low DA available

Excellent stability

Operational >+125° C

Wide range of values

Relatively expensive

Large size

High inductance

Timing and pulse shaping circuits
MOS 0.01% Good DA

Small

Operational above +125° C

Low inductance

Limited availability

Available only in small capacitance values

 
Polycarbonate 0.1% Good long-term stability

Low cost

Wide temperature range

Large size

DA limits to 8-bit applications

High inductance

Timers, filters and applications in high ambient temperature
Polyester 0.3%

to 0.5%

Moderate stability

Low cost

Wide temperature range

Low inductance (stacked film)

Self-healing

Large size

DA limits to 8-bit applications

High inductance

Bypassing and coupling
Mica >0.003% Low loss at HF

Low inductance

Very stable

Available in 1% values or better

Quite large

Low values (<10 nF)

Expensive

 
Aluminum Electrolytic High Large values

High currents

High voltages

Small size

High leakage

Usually polarized

Poor stability

Poor accuracy

Inductive

 
Tantalum Electrolytic High Small size

Large values

Medium inductance

High melting point

High dielectric strength

Good ductility

Quite high leakage

Usually polarized

Expensive

Poor stability

Poor accuracy

 

 

Related Pages on RF Cafe

- Capacitors & Capacitance Calculations

- Capacitor Color Codes

- Capacitance Conversions

- Capacitor Dielectrics

- Standard Capacitor Values

- Capacitor Vendors

- The Noble Art of De-Coupling

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